The present invention relates to an image processing apparatus which optimally processes image information of an original read by a scanner in accordance with the image characteristics thereof.
In image forming apparatuses such as copy machines, an image is read by an image reading unit as a digital signal, and the digital signal is supplied to a recording unit so as to obtain a reproduced image on a hard copy. In such an image reading unit, an original is read out by an image sensor such as a CCD (Charge Coupled Device) image sensor by dividing the image into small areas, that is, pixels. An analog electric signal obtained by the image sensor is converted into a digital signal, and then various image processing operations are applied to the digital signal so as to obtain optimum image data in accordance with the image characteristics thereof.
In this type of image forming apparatus, an original is read out by a line sensor or the like having a small pixel size. Accordingly, when intensity change of the original image has periodicity such as in a half tone image, there is a possibility of formation of moire in a recorded image due to interference of the periodicity of the intensity change of the original image with the pitch of the image sensor arranged in the line sensor, that is, the sampling period. This moire can be eliminated by suppressing the periodicity of the intensity change through a plurality of pixels by averaging the intensity of the pixels.
However, when intensities of a plurality of pixels are averaged to eliminate a moire, the resultant character image or continuous-tone image may be undesirably blurred. Therefore, there is a problem in that when a mesh image and a character image or a continuous-tone image are mixed in one original image, the averaging process must be applied only to the mesh image area.